Increase in the plasma levels of the N-terminal and C-terminal portions of the prohormone of atrial natriuretic factor during normal pregnancy

Abstract

The influence of pregnancy on the circulating concentrations of atrial natriuretic factor, the 28 amino acid carboxy (C)-terminal end of the 126 amino acid atrial natriuretic factor prohormone, and the amino (N)-terminus of the prohormone was studied with three specific radioimmunoassays recognizing: (1) atrial natriuretic factor (i.e., amino acids 99 through 126), (2) the 98 amino acid N-terminus, and (3) amino acids 31 through 67 from the midportion of the N-terminus of the prohormone. Plasma atrial natriuretic factor in normal pregnant women gradually increased as pregnancy progressed, with the mean -t SEM being 58 ± 4 pg/ml in the first trimester, 74 ± 5 pg/ml in the second trimester, and 89 ± 7 pg/ml in the third trimester. Likewise, proatrial natriuretic factor 31 through 67 increased from 1421 ± 76 pg/ml (first trimester) to 1509 ± 84 pg/ml (second trimester) to 1758 ± 83 pg/ml in the third trimester, whereas the whole N-terminus of the prohormone increased from 1804 ± 98 pg/ml (first trimester) to 1909 ± 111 pg/ml (second trimester) to 2160 ± 79 pg/ml in the third trimester. These results suggest that release of the N-terminus of the prohormone, as well as atrial natriuretic factor, increases with the rise in blood volume associated with a normal pregnancy. The circulating concentrations of both the C-terminus and N-terminus of the atrial natriuretic factor prohormone increased further in the 48 hours after delivery. Because both the C-terminus and N-terminus of the atria[ natriuretic factor prohormone contain diuresis-producing peptides, these results suggest that postpartum diuresis may be mediated by these peptides.